1. The Field of the Invention
This invention relates to primary and secondary batteries for use downhole for powering a telemetry network and other downhole tools. More specifically, this invention relates to a battery or a fuel cell having internal components that are pressurized to the ambient pressure found downhole, to depths of 20,000 feet or more, in order to compensate for downhole thermal conditions above 120° C.
2. The Relevant Art
At depths of 20,000 feet or more, temperature and pressure may reach levels of 200° C. and 10,000 PSI, respectively, providing a hostile environment to downhole drilling components. Moreover, as drilling methods and equipment become more advanced and accurate, newer and more advanced components are continuously being upgraded to perform various functions. Since reliable power may not be readily transmitted to downhole drilling environments, batteries may be used to provide power to various components. Nevertheless, very few batteries are designed to operate in the types of conditions encountered downhole. Moreover, due to space constraints, very few batteries have the desired power densities and dimensions to fit within spaces available in downhole equipment.
For example, few if any batteries are known to operate at temperatures in excess of 170° C. The majority of batteries are designed to function in conditions below 100° C. Thus, very few batteries currently available may be used to provide reliable power sources to downhole drilling components. Thus, apparatus and methods are needed to provide reliable power to downhole components.
The factors affecting downhole pressure are generally the depth of drilling, the hardness and continuity of the subterranean formations being drilled, the composition of the drilling fluid being used, and the under-balanced condition maintained in the well bore. Similar factors are also relevant to the temperature in the well bore. Extreme pressure and thermal conditions in deep wells contribute to premature battery degradation in downhole applications.
Generally, downhole batteries are self-contained in their own sealed containers to protect them from ambient conditions, including high pressure and temperature. The need to protect battery components from external pressure may require an expensive pressure housing in the downhole tool. In addition, physical constraints imposed by the geometry of a downhole tool often means that a battery must intrude on the flow space within the tool, or it must be limited to relatively small diameters, reducing overall power density. Moreover, high-pressure housings are always subject to leakage that may lead to a catastrophic failure of a battery and may damage surrounding electronic components as well.
U.S. Pat. No. 6,187,469, to Marincie et al., incorporated herein by reference, is an example of a downhole battery system. Marincie et al. teaches individual cells mounted end to end and interlocked together to prevent rotation of cells relative to one another. The cells are electrically connected and mounted between an inner and outer tube. The housing for the battery is sufficiently strong to resist downhole pressures and is provided with vents for the discharge of gases.
U.S. Pat. No. 6,224,997, to Papadopoulos, incorporated herein by reference, teaches a flexible battery pack for powering downhole electronic equipment. The pack includes a plurality of electrochemical cells connected and tied together in a stacked relationship by a pair of semi-cylindrical encapsulating shells which form a primary containment for the cells. The shells comprise a glass fiber reinforced plastic material. The primary containment is sealed within a stainless steel tube that is provided to hold the components in place during operation. Electrical conductors are also provided to transmit energy from the battery to selected downhole equipment. Each cell is sealed to resist the downhole environment and a venting mechanism is provided.
U.S. Pat. No. 4,087,590, to Kraft, discloses a pressure-equalized electrochemical battery system. Kraft discloses a pack of ordinary, commercially available batteries that are provided with a common electrolyte-filled reservoir coupled to each battery by a small tube. The reservoir includes a compliant diaphragm which, when exposed to pressure, applies the pressure to the reservoir of electrolyte to force it into the battery. Forceful filling of the cells equalizes their internal and external pressures. Kraft is intended for deep-sea applications and would not meet the constraints of a downhole tool string.
U.S. Pat. No. 6,117,583, to Nilsson, discloses a battery that is intentionally pressurized, but is pressurized above ambient pressure. In lead-acid batteries, PbSO4 that is formed during discharge has a higher volume than Pb and PbO2 from which it is formed. When it is discharged, the shrinkage causes a loss of contact between active components and the current conducting lead frame. This is overcome by providing a strong housing that keeps the battery under high pressure.
U.S. Pat. No. 6,253,847, to Stephensen, discloses a permanent downhole power source for a producing well using a steel casing coated with iron oxide as a cathode. Fe2O3 is reduced to FeO. A separate piece of Zinc, as an anode, is provided which corrodes and is consumed. A cement treated with additives, to increase its conductivity, serves as an electrolyte.
In view of the foregoing, what is needed is a long life battery that will accommodate the temperature, pressure, and physical constraints of downhole tools and be functional to depths of 20,000 feet or more.